You can't replace just "the bulb". The Pacifica uses an LED "bar"
inside of the lamp unit. It must be replaced as a single piece.
You may have to remove the entire rear spoiler to get at it. If you're
not mechanically inclined, it's best to take it to the dealer or a shop for
the repair. It's pretty labor intensive and requires removing "other" non-
related parts (including parts for the rear window wiper/washer and
others.